Through-substrate via formation with improved topography control

ABSTRACT

A device include a substrate and an interconnect structure over the substrate. The interconnect structure comprising an inter-layer dielectric (ILD) and a first inter-metal dielectric (IMD) formed over the ILD. A through-substrate via (TSV) is formed at the IMD extending a first depth through the interconnect structure into the substrate. A metallic pad is formed at the IMD adjoining the TSV and extending a second depth into the interconnect structure, wherein the second depth is less than the first depth. Connections to the TSV are made through the metallic pad.

BACKGROUND

Three-dimensional integrated circuits (3DIC) and stacked dies are commonly used to decrease the overall size of integrated circuits. 3DICs and stacked dies use through-substrate vias (TSVs, also referred to sometimes as through silicon vias or through vias) to connect an individual die through its backside to another die. By using vertical space, 3DICs and stacked dies are able to reduce the overall footprint of an integrated circuit. Additionally, TSVs are used to create short grounding paths through the backside of a die, which is typically covered with grounded aluminum film. However, as improvements in technology continually decrease the size of integrated circuits and its constituent components, controlling the topography of the layers in a die becomes increasingly important.

In a typical die, a substrate comprising active devices, such as transistors, is provided, an inter-layer dielectric (ILD) is formed over the substrate, and then any number of inter-metal dielectrics (IMDs), comprising metallic trenches/vias used to execute logic functions, are formed over the ILD. In a 3DIC or stacked die, a TSV may also be formed at either the ILD or an IMD. The ILD acts as a barrier between the active devices in the substrate and the metallic trenches/vias in the IMD. The ILD prevents metallic particles in the IMD from diffusing into the substrate and is crucial to the proper functioning of the active devices in the substrate.

When formed at the ILD layer, the TSV may be covered with a liner and a metal pad in the subsequent IMD layer. The liner and pad act to create a flat top surface for stable connections to the TSV. Using this method, the ILD often suffers loss due to erosion and dishing caused by the TSV's formation process. ILD loss is especially problematic for advanced technologies where the die components are so compact and precise that tolerance for such loss is very limited. Furthermore, the use of a liner causes high contact resistance between the TSV and the overlying metal pad. On the other hand, formation of the TSV at the IMD layer suffers from issues of uneven topography due to TSV's size and grain growth. This uneven topography can lead to broken and unstable connections to the TSV.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present embodiments, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIGS. 1A through 1G are cross-sectional views of intermediate stages of manufacture of a wafer comprising a TSV and a topographically flat portion of the TSV in accordance with various embodiments;

FIGS. 2 and 3 illustrate top-down views of the TSV in the wafer from FIGS. 1A-1G according to various embodiments;

FIGS. 4A through 4D are cross-sectional views of intermediate stages of manufacture of a wafer comprising a TSV and a metal pad overlying the TSV in accordance with various embodiments;

FIG. 5 shows a cross-sectional view of another wafer comprising a TSV and a metal pad overlaying the TSV according to various embodiments; and

FIGS. 5A and 5B illustrate top-down views of the metal pad in the wafer from FIG. 5 in accordance with various embodiments.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the present embodiments are discussed in detail below. It should be appreciated, however, that the present disclosure provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the disclosed subject matter, and do not limit the scope of the different embodiments.

With reference now to FIG. 1A, wafer 100, which includes substrate 102, is provided. Substrate 102 is preferably a semiconductor substrate, suck as a bulk silicon substrate, although it may include other semiconductor materials such as group III, group IV, and/or group V elements. Integrated circuit 110, shown as transistors, and isolation fields 112 are formed on the top surface of substrate 102. Interconnect structure 104 has been formed over the top surface of substrate 102. Interconnect structure 104 includes inter-layer dielectric (ILD) 106 formed of low-k dielectric materials having k values, for example, lower than about 4.0. Contact plugs 114, made of tungsten or other similar metallic material, may be formed within ILD 106. Furthermore, interconnect structure 104 includes inter-metal dielectric (IMD) 108 containing trenches/vias 116. IMD 108 may be formed low-k dielectric materials having low k values, for example, lower than about 4.0. IMD 108 and ILD 106 could be, for example, silicon oxide, SiCOH, and the like. Trenches/vias 116 may be made of copper or copper alloy although other metals such as, aluminum, silver, gold, or combinations thereof, may also be used. The embodiment depicted in these figures show interconnect structure 104 as having only one IMD layer 108. It is contemplated in other embodiments that interconnect structure 104 will have multiple IMD layers.

FIG. 1B shows the formation of photo resist layer 118 over the top surface of IMD 108 in wafer 100. Photo resist layer 118 is patterned to create an opening of width W1 over IMD 108, using known photolithographic techniques.

Referring to FIG. 1C, a first etch is performed to create opening 120, extending a depth of D1, through interconnect structure 104, into substrate 102, using known etching techniques. In one embodiment of this invention, photo resist layer 118 is removed after this first etch process.

FIG. 1D shows the formation of a second photo resist layer 122 on the top surface of IMD 108 in wafer 100. Photo resist layer 122 is then patterned to have an opening 124, overlaying opening 120. Opening 124 has a width W2. Typically, width W2 will be larger than width W1. For example, in an embodiment, width W1 would be between about 5 μm and 10 μm, whereas width W2 would be between about 5.5 μm and 20 μm.

Referring to FIG. 1E, a second etch is performed, which expands opening 120 to include opening 126. This second etch extends a depth D2 into interconnect structure 104. Depth D2 is smaller than the depth D1 created during the first etch. The second etch does not extend into substrate 102. In a typical embodiment, depth D2 would be less than about 1 μm. While opening 126 is shown as extending into the top portion of ILD 106, it is contemplated that opening 126 would not reach ILD 106 in other embodiments. Following this second etch, photo resist layer 122 is removed.

In an alternative embodiment of this invention, photo resist layer 118 remains on IMD 108 after the first etch process. In this alternative embodiment, photo resist layer 118 undergoes a second patterning process after the first etch. The patterning process would remove the areas similar to those removed in photo resist layer 122 discussed above. A second etch, similar to the one discussed above, would then be performed, and photo resist layer 118 would then be removed.

In FIG. 1F, opening 120 and opening 126, are filled with a metallic material forming through-substrate via (TSV) 128. In various embodiments, the filling material includes copper or copper alloys, although other metals such as aluminum, silver, gold, and combinations thereof, may also be used. The formation method of TSV 128 may include printing, electro plating, electroless plating, and the like. Prior to filling, a barrier layer, a liner, and/or a seed layer (not shown) may be formed within the openings 120 and 126, as known in the art. After opening 120 is filled, the metallic material is planarized using the well-known chemical mechanical polish (CMP) method to remove excess material. By forming TSV 128 at the top surface of IMD 108 instead of ILD 106, ILD loss due to erosion and dishing caused by the CMP process is avoided.

Furthermore, planarization at an IMD layer allows for the use of dummy metals during the CMP process. Dummy metals are non-functional features that do not contribute to the logic design of a wafer. These dummy metals act as a buffer during the CMP process, allowing for better erosion and dishing control during CMP. Furthermore, the metal density of a surface directly affects the rate at which the surface is planarized through CMP. Varying metal densities may lead to uneven topography after planarization. To address this problem, dummy metals are used to fill low metal density areas and create uniform metal densities across a surface. Therefore, it is known in the art to include dummy metals in IMD layers to aid the CMP process. However, dummy metals are generally unavailable at the ILD layer. By forming TSV 128 at IMD 108, dummy metals may be used during CMP. Accordingly, the resulting dishing and erosion at IMD 108 would be less than the dishing and erosion a similar CMP process would have caused at ILD 106.

FIG. 1G shows the same wafer 100 as the wafer shown in FIG. 1F. However, for the sake of clarity, TSV 128 is shown as being divided into two regions: 130 and 132. It is noted that in TSV 128, the top surface of region 130 will be topographically flatter than the top surface of the region 132. This difference in topography is due to region 130, extending depth D2, being relatively shallow compared to region 132, extending depth D1. It has been observed that by keeping depth D2 under 1 μm, the surface topography of region 130 can be kept relatively flat. Any connections (not shown) to TSV 128 will be made to this topographically flatter region 130. By connecting to this topographically flat region 130, issues involving broken connections can be avoided allowing for more reliable connections to TSV 128. This method also eliminates high contact resistance caused by any liner, barrier, or seed layers between a TSV formed at ILD 106 and any overlaying metal features in IMD 108.

Now referring to FIG. 2, a top-down view of TSV 128 is shown. Region 130 is shown to be encompassing region 132, which corresponds to regions of TSV 128. Any connections to TSV 128 would be made to region 130. While FIG. 2 shows region 130 as rectangular, alternative shapes, such as circular or ovular, for region 130 are also contemplated in other embodiments. Furthermore, region 130 need not encompass region 132 as shown in FIG. 2. Region 130 need only adjoin region 132. For example, FIG. 3 shows an alternative embodiment where region 130 is ovular and merely adjoins region 132 instead of encompassing region 132.

In the embodiment shown in FIGS. 1A-1G, TSV 128 is shown as being formed on IMD 108. IMD 108 being the first IMD layer formed above ILD 106 in interconnect structure 104. It is contemplated, in other embodiments of this invention, to form TSV 128 on other IMD layers (not shown) in interconnect structure 104.

Now referring to FIG. 4A, an alternative embodiment of the invention is shown. FIG. 4A shows wafer 200. Wafer 200 contains substrate 202 and interconnect structure 204. Interconnect structure 204 contains ILD 206. Substrate 202 and ILD layer 206 is substantially similar to substrate 102 and ILD layer 106 in wafer 100 described above. Thus detailed descriptions of these features are omitted.

Wafer 200 was formed using a single-damascene process as opposed to a dual-damascene process. In a typical dual-damascene process, vias and trenches in a layer are formed simultaneously; therefore, a typical IMD layer may contain both trenches and vias. In a single-damascene process, trenches and vias are formed separately. Therefore interconnect structure 204 contains IMD layers formed separately as: trench layer 208, containing trenches 212, and via layer 210, containing vias 214. IMD layers 208 and 210 may all be made of low-k dielectric materials, for example, doped silicon glass, SiCOH, SiON, and the like. Trenches 212 and vias 214 may be made of copper, copper alloys, or any combination thereof. The embodiment of invention illustrated in FIG. 4A only contains one IMD trench and one IMD via layer. However, in other embodiments, interconnect structure 204 could contain any number of IMD trench layers and alternating IMD via layers.

Wafer 200 also contains TSV 216. TSV 216 is analogous to region 132 of TSV 128 in wafer 100. TSV 216 does not contain the portion of TSV 128 referred to as region 130. TSV 216 was formed using a substantially similar process as that used form TSV 128. Therefore, in-depth discussion on the formation of TSV 216 is omitted. Because TSV 216 is formed in IMD via layer 210, ILD loss due to dishing and erosion caused by the CMP process is avoided. Furthermore, dummy metals may be used to aid the CMP process because TSV 216 is formed at IMD 210. While TSV 216 is shown to be formed on the first via layer above substrate 202, TSV 216 may be formed on any other IMD via layer (not shown) in interconnect structure 204.

Now referring to FIG. 4B, another IMD trench layer 218 has been formed on the top surface of IMD via layer 210. IMD trench layer 218 may be made of low-k dielectric materials similar to those used to make IMDs 208 and 210. IMD 218 contains trenches 222 which are similar to trenches 212 in IMD 208. Opening 220 has been formed in IMD trench layer 218 to overlay TSV 216. Opening 220 may be formed using, for example, a combination of photolithography and etching similar to what has been previously described.

FIG. 4C shows the formation of liner 224 in opening 220. Liner 224 covers the both the lateral and vertical surfaces of opening 220. Liner 224 may be made of titanium, titanium nitrate, tantalum, tantalum nitrate, or other like material.

Now referring to FIG. 4D, opening 220 is then filled to form metal pad 226. Pad 226 may be formed using the same metallic materials used to form trenches 212 and 222. Pad 226's top surface is topographically flat due to liner 224 overlying TSV 216. Liner 224 also serves to prevent migration of metallic particles from pad 226 into the neighboring dielectric material in IMD 218. Reliable connections to TSV 216 may be made through the topographically flat pad 226. While the current embodiment describes the separate formation of trenches 222 and pad 226, these features may also be formed simultaneously.

FIG. 5 shows another alternative embodiment of the invention. FIG. 5 shows wafer 300, which has been formed using a single-damascene process similar to the one used to form wafer 200. Wafer 300 contains substrate 302 and interconnect structure 304. Interconnect structure 304 contains ILD 306; IMD trench layers 308 and 312; and IMD via layer 310. Wafer 300 is analogous to wafer 200 in its formation process; therefore, detailed description of the process is omitted. However, several key differences between wafer 300 and wafer 200 and their corresponding features should be noted.

TSV 314 is formed at IMD trench layer 308. TSV 314 is not formed at an IMD via layer. Following the formation of TSV 314, IMD via layer 310 is formed containing pad 318 and vias 320. Also, liner 316 has formed to surround pad 318. Pad 318 and vias 320 may be formed simultaneously using a single-damascene process. The top surface of pad 318 is topographically flat due to liner 316 overlaying TSV 314. Liner 316 is analogous to liner 224 in wafer 200. Further IMD layers may be built on IMD via layer 310, such as IMD trench layer 312, as shown in FIG. 5.

Because pad 318 and vias 320 may be formed simultaneously, pad 318 must be configured to adhere to any design rule limitations related to via formation. Referring now to FIG. 5A, a top-down view of pad 318 in IMD via layer 310 is shown. A circular region 322 corresponds to the location of TSV 314. Pad 318 is shown as overlaying region 322. In the embodiment illustrated in FIG. 5A, pad 318 is shown in a slot configuration. Alternatively, pad 318 may be a configured as a solid square, as shown in FIG. 5B; in a grid pattern, not shown; or any other suitable configuration. The configuration of pad 318 may be altered to adhere to any design rule limitations on IMD via layer 310.

In other embodiments, TSV 314 may be formed at any other IMD trench layer in interconnect structure 304. In these alternative embodiments, cap 318 would be formed on the IMD via layer directly above the IMD trench layer in which TSV 314 was formed. Furthermore, in other embodiments, IMD via layer 310 and IMD trench layer 312 may be formed simultaneously using a dual damascene process. In such cases, liner 316 may extend into IMD trench layer 312 and up the sidewalls of any trench overlaying pad 318.

Although the present embodiments and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the disclosure as defined by the appended claims.

Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present disclosure. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. 

What is claimed is:
 1. A method comprising: forming an interconnect structure over a semiconductor substrate, wherein the interconnect structure comprises an inter-layer dielectric (ILD) and an inter-metal dielectric (IMD) over the ILD; forming a first opening extending a first depth through the interconnect structure and into the semiconductor substrate; forming a second opening contiguous with and wider than the first opening and extending a second depth into the interconnect structure, wherein the second depth is smaller than the first depth; and filling the first opening and the second opening with a metallic material to form a conductive plug having a substantially planar surface at a top of the second opening.
 2. The method according to claim 1, comprising the further step of forming a connection to the conductive plug at the substantially planar surface.
 3. The method according to claim 1, wherein the second depth is less than about 1 μm.
 4. The method according to claim 1, wherein: the step of forming a first opening comprises: forming a first photo resist layer over the first IMD and patterning the photoresist layer so that the photo resist layer comprises a first photo resist opening having a first width; and the step of forming a second opening comprises: forming a second photo resist layer over the first IMD and patterning the photoresist opening to form a second photo resist opening having a second width, the second photoresist opening overlaying the first opening.
 5. The method according to claim 4, wherein the first photoresist layer and the second photo resist layer are the same photo resist layer.
 6. The method according to claim 4, wherein the first width is smaller than the second width.
 7. The method according to claim 1, wherein the IMD layer comprises a dummy metal.
 8. The method according to claim 1, wherein the second opening is configured in a pattern consisting essentially of a rectangle, a circle, an oval, and combinations thereof.
 9. A method comprising: forming an interconnect structure over a semiconductor substrate, wherein the interconnect structure comprises: an inter-layer dielectric (ILD) and a first inter-metal dielectric (IMD) formed over the ILD, wherein the first IMD comprises a first metallic component; forming a conductive plug at the first IMD extending into the interconnect structure and the semiconductor substrate; forming a second IMD over the first IMD, wherein the second IMD comprises a second metallic component; forming an opening in the second IMD extending to the first IMD and overlaying the conductive plug and the first IMD; forming a liner in the opening, wherein the liner covers both the bottom surface and the sidewalls of the opening; and depositing a metallic material into the opening to form a pad.
 10. The method according to claim 9, wherein: the first IMD is an IMD via layer and the first metallic component is a via formed using a single damascene process; and the second IMD is an IMD trench layer and the second metallic component is a trench formed using a single damascene process.
 11. The method according to claim 9, wherein: the first IMD is an IMD trench layer and the metallic component is a trench; and the second IMD is an IMD via layer and the second metallic component is a via.
 12. The method according to claim 11, wherein forming the via in the second IMD and depositing a metallic material into the opening to form a pad are performed simultaneously.
 13. The method according to claim 9, wherein the opening is configured in a pattern consisting essentially of a rectangle, a circle, an oval, and combinations thereof.
 14. The method according to claim 9, wherein the opening is configured in a slot pattern.
 15. The method according to claim 9, wherein the first IMD layer comprises a dummy metal.
 16. The method according to claim 9, wherein the liner is a material selected from the group consisting essentially of titanium, titanium nitrate, tantalum, tantalum nitrate, and combinations thereof.
 17. A method comprising: forming a transistor device in a semiconductor substrate; forming an inter-layer dielectric (ILD) over the semiconductor substrate and the transistor device; forming an inter-metal dielectric (IMD) over the ILD; forming interconnects in the ILD and the IMD; patterning the ILD, the IMD, and the substrate to form a first opening extending a first depth substantially into the substrate from a top surface of the IMD; patterning at least the IMD to form a second opening in the IMD contiguous with and wider than the first opening and extending a second depth from the top surface of the IMD, the second depth being different than the first depth; simultaneously filling the first opening and the second opening with a conductor; and planarizing a top surface of the conductor.
 18. The method of claim 17 wherein the first opening has a first lateral dimension parallel to a major surface of the substrate, the second opening has a second lateral dimension parallel to the major surface of the substrate, and the second lateral dimension is greater than the first lateral dimension.
 19. The method of claim 17, wherein the first opening extends substantially into the substrate and the second opening extends to an interface between the ILD and the IMD.
 20. The method of claim 17, wherein the first opening is a circular shape when viewed from a top down and the second opening has a non-circular shape when viewed from a top down. 